Article citation info: 85

Roczek K, Krol A, Fidali M, Rogala R. A hybrid diagnostic system of main drive of industrial press line. Diagnostyka. 2021;22(1):85-92.

https://doi.org/10.29354/diag/133211

DIAGNOSTYKA, 2021, Vol. 22, No. 1

ISSN 1641-6414 e-ISSN 2449-5220

DOI: 10.29354/diag/133211

A HYBRID DIAGNOSTIC SYSTEM OF MAIN DRIVE

OF INDUSTRIAL PRESS LINE

Krzysztof ROCZEK 1, Adrian KROL

2, Marek FIDALI

3, Tomasz ROGALA

4

1 Silesian University of Technology, krzysztof.roczek@opel-vauxhall.com 2 Silesian University of Technology, adrian.krol@polsl.pl

3 Silesian University of Technology, marek.fidali@polsl.pl 4 Silesian University of Technology, tomasz.rogala@polsl.pl

Abstract

The idea of Industry 4.0 indicates Condition Based Maintenance (CBM) and Predictive Maintenance

(PdM) as fundamental maintenance strategies in modern factories. CBM and PdM could be implemented with

use of on-line continuous monitoring and diagnostic systems and also as a program of systematic

examinations of asset condition done by maintenance personnel. Using data collected from hand held

instruments and from on-line systems it is possible to build full image of current asset condition and predict

probable faults in the future. This paper presents system of condition monitoring and diagnosing of main

drive of industrial press line. The system uses diagnostic data coming from different sources like vibration,

electrical and thermal measurements. Application of different types of data makes the system hybrid and

allows improve diagnostic inference process. The article describes how the system is designed and

implemented.

Keywords: MFMEA, CBM, press drive, diagnostics, vibration, MCSA, monitoring system

HYBRYDOWY SYSTEM DIAGNOSTYCZNY NAPĘDU GŁÓWNEGO

PRZEMYSŁOWEJ LINII PRAS

Streszczenie

Idea Przemysłu 4.0 wskazuje Condition Based Maintenance (CBM) oraz Predictive Maintenance (PdM)

jako podstawowe strategie służb utrzymania ruchu w nowoczesnych fabrykach. CBM i PdM mogą zostać

wdrożone z wykorzystaniem ciągłego monitoringu w trybie online oraz systemów diagnostycznych, a także

systematycznej kontroli stanu urządzenia przeprowadzanej przez personel utrzymania ruchu. Używając

danych zgromadzonych za pomocą przyrządów ręcznych, a także systemów pracujących w trybie online

możliwym jest zbudowanie kompletnego obrazu aktualnego stanu urządzenia i przewidywanie potencjalnych

awarii w przyszłości. Poniższa publikacja opisuje system diagnostyczny przemysłowej linii pras. System

wykorzystuje dane pochodzące z różnych źródeł: drgania, natężenie prądu elektrycznego i pomiarów

temperatury. Różnorodność danych sprawia, że system staje się hybrydowy, co pozwala usprawnić

wnioskowanie diagnostyczne. Artykuł opisuje proces projektownia takiego systemu oraz jego implementację.

Słowa kluczowe: MFMA,CBM, MCSA, metody diagnostyczne, napęd prasy

1. INTRODUCTION

Metal stamping is commonly used in the

automotive industry. The stamping process is

carried out on the press lines which could be treated

as a critical industrial object due to extremely high

costs of production losses caused by press line

breakdown. The reasonable way of avoiding

unexpected press line breakdowns is application of

Condition Based Maintenance (CBM) and

Predictive Maintenance (PdM). CBM and PdM are

ideas known for many years. However, since the

trend of Industry 4.0 is currently so popular the two

aforementioned could be treated as the fundamental

strategies in modern factories including stamping

departments. CBM and PdM could be based on

continuous monitoring and diagnosis systems.

Contemporary market offers solutions for press line

condition monitoring. There are solutions offered

by press lines manufacturers [12] or automation and

measurement systems manufacturers [10, 13, 14].

Scientific researches indicate modern solution for

stamping monitoring based on tooling integrated

sensors [16] or press tonnage sensors. Interesting

solution integrating different sources of information

for press condition monitoring was proposed by

Fraunhofer Institute for Machine Tools and

Forming Technology [14]. Currently available

commercial systems can be used for the purpose of

press condition monitoring. One of them is SIPLUS

system invented by Siemens company [17]. Data

analysis is performed in accordance to ISO 10816-3

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Roczek K, Krol A, Fidali M, Rogala R.: A hybrid diagnostic system of main drive of industrial press line

86

standard which is related to vibration analysis. In

this system it is possible to add analog inputs

module and perform measurement of any other

physical quantity with use of analog output sensor.

Products of ifm electronic [18] are also based on

vibration measurement. The system provides motor

diagnosis techniques, limited to signals coming

from accelerometers. Similar solution was

developed by TURCK [19]. A really interesting

solution is delivered by ABB - AbilityTM Smart

Sensor for motors. Sensors are easily mounted to

the motor housing and may provide basic data (i.e.

temperature) about motor condition to the system

with use of Wi-Fi system. One may see that there

are many possibilities of condition monitoring

systems that can be applied also for press drive

system. Most of them perform either vibration or

temperature analysis. Of course, advanced

frequency inverters also provide possibility of

current measurement. It is possible to calculate

frequency spectrum of motor current, without

implementation of MCSA. Despite the large

availability of comprehensive diagnostic solutions

supporting CBM and PdM they are rarely used due

to the lack of sufficient knowledge in maintenance

departments or/and high costs inadequate to

application in old press lines working in many

companies for years.

Due to the fact that there are many papers [2, 5,

6, 8] that provide information on capabilities and

suitability of MCSA it was decided to invent own

diagnostic system.

This paper presents concept of condition

monitoring and diagnosing system dedicated for

industrial press line based on data coming from

different sources like vibration, electrical and

thermal measurements what makes the system

hybrid and allows improve diagnostic inference

process. The paper focuses on currently

implemented subsystem allowing monitoring and

diagnosing press main drive with use of electrical

and vibration parameters.

2. PRESS LINE AS A COMPLEX OBJECT

FOR CONDITION MONITORING

In stamping process different types of presses

are used. Generally, the three main types of presses

are in use: mechanically-, hydraulically- and

servodriven ones. The most common are

mechanical presses which are assembled into lines

operating in different ways. The condition

monitoring system described in the article concerns

tandem press line with mechanical presses. It is

characteristic for this type of press line that each

station (press) has its own, individual drive system.

Fig. 1 presents the diagram of tandem press line

with an exit conveyor. Basically, the following

subsystems can be distinguished in most of press

lines:

cushion (hydraulic or pneumatic);

hydraulic unit (for lubrication and power

hydraulic unit);

drive system with main motor, shaft, gears,

connecting rods, clutch and brake;

counterbalance system;

slide adjustment;

controls system with safety subsystems;

parts transport system;

pneumatic system;

front of line with de-stacking unit and centering

station;

end of line with conveyor, collecting chute or

automatic racking system;

slide system with clamping units

moving bolsters and bed unit

The press line is a complex system where any

fault could influence the whole stamping process

and in some cases cause unexpected breakdown of

the line.

Fig. 1. Diagram of tandem press line [21]

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Roczek K, Krol A, Fidali M, Rogala R.: A hybrid diagnostic system of main drive of industrial press line

2.1. Criticality analysis of press line

Considering press line from operational point of

view it has a serial structure where breakdown of

any link of the chain cause stoppage of the whole

line. Due to the complexity of the press line it was

necessary to point out critical elements which will

be monitored and diagnosed continuously. Defining

the most important parts of the press line could be

based on the criticality analysis. This method

allows to point out the elements that are most

critical for production stability. Criticality analysis

gave a good basis for further design process of

condition monitoring system. There are many

methods that can be implemented for that purpose,

like AHP (Analytic Hierarchy Process) [17], ABC

(Activity Based Costing) [18] or MFMEA

(Machinery Failure Mode and Effects Analysis) [2].

During designing of condition monitoring systems

of press line the authors were basing on MFMEA

which allows to assign the problem to particular

element of the analysed object. The method

requires the following steps to be undertaken [19]:

identification of equipment and its mode of

operation;

indication of potential failures and their root

causes;

analysis of failure effects on particular object

component with use of Severity, Probability and

Detectability coefficients;

measurement of potential effects of the failure

modes based on Risk Priority Number (RPM) as

a product of Severity, Probability and

Detectability coefficients.

The result of the analysis indicates components

of the objects in order of their criticality. This gives

the opportunity to simplify prioritization of

necessary actions to reduce probability of failure.

Analysis of the press line was performed on the

basis of historical data derived from the

maintenance reports. Table 1 presents a part of

MFMEA evaluation that was performed for the

stamping press. In that particular case the most

critical subsystem for this machine is the main

drive. In the considered case the main drive consists

of an induction motor, a set of bearings and a shaft

between the motor and the flywheel.

2.2. Main drive system of press line

MFMEA evaluation indicates that main drive

system is critical for reliability of the whole press

line. Each station of the tandem press line is

equipped with its own main drive system. In such

situation it is necessary to diagnose each of them.

However, the structure of condition monitoring

system can be similar for all the above mentioned

drives. This results from similar design of those

drive systems. In fig. 2 an exemplary press main

drive system and its parameters were presented.

From the diagnostic point of view one may

distinguish several main components of drive

system: main motor, elastic coupling, bearing set of

belt drive and shaft with the pulley.

4. THE HYBRID CONTINUOUS CONDITION

MONITORING SYSTEM OF THE MAIN

DRIVE OF THE PRESS LINE

Due to the press line complexity and criticality a

general concept of monitoring and diagnosing

system was proposed. Structure of the system is

presented in fig. 3. The main part of the system is

the data base server, whose main task is to collect,

process and share data between subsystems as well

as enterprise divisions. A distributed structure of

subsystems responsible for each part of press line

was assumed. Subsystems can be divided into

automated and personnel driven ones. Condition

monitoring and diagnosing subsystems of each

press and transfer equipment are automated what

means that they are able to diagnose and predict

how asset condition will change in the future.

Information about past, present and future asset

condition is shared to each subsystem including

maintenance department. Maintenance personnel

are responsible for detailed manual inspection of

the press line suspicious areas to confirm

correctness of diagnosis performed by automated

system as well as for planning repairs.

Table 1. Part of MFMEA – own evaluation

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The focus of system development was to design

subsystem of condition monitoring and diagnosing

of single press. General structure of such subsystem

is presented in fig. 4. Subsystem of condition

monitoring system consists of main drive system,

hydraulic system, stamping and synchronization

system, material transfer system. Due to high

criticality a condition monitoring and diagnosis

system of main drive was designed and launched at

first. Logical structure of the system is presented in

fig. 5.

Fig. 2. General structure of the analyzed press main drive system

Fig. 3. General structure of press line diagnostic system

Fig. 4. General structure of single press diagnostic system

Fig. 5. Structure of condition monitoring system of press main drive

DIAGNOSTYKA, Vol. 22, No. 1 (2021) 89

Roczek K, Krol A, Fidali M, Rogala R.: A hybrid diagnostic system of main drive of industrial press line

Evaluation of main drive condition is based on

data acquired from simultaneous measurements of

vibration, electrical current and temperature. Data

from each measurement system is transferred to

data acquisition, processing and analysis system

where condition evaluation connected with fault

detection and classification are performed

independently for each type of measured data.

Results of condition evaluation are agreed upon

additional data from maintenance services and

sending to local decision support system.

Information concerning main drive condition,

warnings, alarms and suggestions about further

operational decisions are transferred by DeviceNet

to press control system and by Ethernet to main

data base server, and is shared with another press

line condition monitoring and diagnosis

subsystems. The system server allows to send the

email with information about the detected press

faults and suggestions of further check for

maintenance service.

Connection of monitoring system to existing

press controller was necessary to receive

information about current machine mode of

operation and to send information about the current

status of main dive system. On the basis of the data

taken from press controller it was possible to

synchronise measurements which correspond to

steady state press operation cycle. Stationary

conditions of press operation occur when the slide

is at Top Dead Centre. It assures repeatable

measurements during comparable load conditions

of the press drive.

Hardware part of monitoring system was based

on modular National Instruments Compact RIO

system and software part was developed using

National Instruments LabView development

system.

4.1. Subsystem of electrical parameters based

condition monitoring

A part of monitoring systems based on electrical

parameters measures the intensity of motor electric

current. For measurement purposes the subsystem

used (Fig. 6) consists of electric current transducers

LEM HAT 400-S fixed on inverter output wires

(Fig. 7) supplying electric motor. Current

transducer output signals are inputs of Data

Acquisition Card (DAQ) NI 9215 of Compact RIO

system where they are converted to digital signals

required for further Motor Currents Signature

Analysis (MCSA) purposes. Signal processing and

analysis were performed by dedicated software

developed in LabView and embedded in local

computer of Compact RIO system. An exemplary

screen of the developed software for spectral

analysis of current signal is presented in Fig 9.

Fig. 6. Diagram of press main drive monitoring system

Fig. 7. LEM transducers

Fig. 8. Compact RIO module

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The gathered current signals were 0.2 second

long (20 x 104 samples) and were verified at

stationarity at first. Before further analysis, values

of signals were statistically standardized. Next,

scalar features in time and frequency domain were

calculated. In total, 35 point features in the time

domain and 90 point features in the frequency

domain, were considered [1][2][3]. Some of the

features were calculated based on Fast Fourier

Transform (FFT) of AC level of the current Park’s

vector modulus [4] known as extended Park’s

vector approach (EPVA) [20]. FFT spectra were

estimated and analysed according to methods

described in International Standard ISO

20958:2013 [5]. The standard defines specific

spectral symptoms of such electric motor faults

like: broken bars, rotor eccentricity and bearings

defects. Additionally, total harmonic distortions,

crest factor, impulse factor, form factor, rms, peak-

peak, kurtosis, skewness, smoothing factor and

many other current signal features were also

estimated and monitored.

In fig. 9 screen with MCSA symptoms marked

on the spectrum of Extended Park’s Vector

Approach of current intensity signal was presented.

Different colours were applied to point the

frequency bands where symptoms corresponding to

particular faults can appear in the spectrum.

4.2. Subsystem of vibration based condition

monitoring

The structure of vibration based condition

monitoring subsystem (Fig. 6) includes

accelerometers CTC M/AC240-1D and M/AC154-

1A mounted in bearing housing of motor and belt

drive (Fig. 10a) and DAQ modules (NI 9234)

located in separate Ni Compact RIO chassis (Fig.

10b). Accelerometers measure vibration in radial

and axial directions. Vibration signals are processed

and converted to digital form and then estimated in

time and frequency domain by software developed

in LabView embedded in Compact RIO controller.

The software contains modules for calculation of

classical features like RMS, Peak and Peak to Peak

amplitudes of vibration velocity and acceleration

signals. Scalar features are plotted as time series for

trend analysis and additionally are compared to

limit values according to vibration standards ISO

10816 and VDI 3832. Additionally, velocity and

acceleration signals are transformed to frequency

domain with use of FFT algorithm which allows to

estimate and monitor spectral features connected

with typical mechanical faults like unbalance,

misalignment and belt drive problems. Additional

functions of software allows assessment of bearings

conditions on the basis of envelope analysis of

filtered acceleration signal.

Fig. 9. User interface of current analysis with use of EPVA

Fig. 10a. Accelerometer installed on

motor housing

Fig. 10b. Additional chassis for accelerometers

connection

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Roczek K, Krol A, Fidali M, Rogala R.: A hybrid diagnostic system of main drive of industrial press line

Fig. 11. FFT spectrum of vibration signal before and after replacement of elastic coupling

Different placement, radial and axial, of

vibration sensors were applied. Plots of acceleration

spectra taken from one of sensors before and after

replacement of elastic coupling and bearings are

presented in fig. 11.

5. CONCLUSIONS

This paper presents originally developed hybrid

condition monitoring system of press main drive.

The main parts of the system are subsystems

devoted to the analysis of vibration and electric

current parameters. The current based condition

assessment subsystem is based on originally

developed features useful for diagnosis of most

induction motor faults. During the system operation

it was possible to early detect and repair serious

problems with main drive of the press. It helps

avoid unexpected downtime and production losses.

The presented system is under continuous

development especially in the area of data fusion

and automation of condition assessment. Results of

further research will be published in subsequent

scientific papers.

ACKNOWLEDGEMENTS

Described herein are selected results of study,

supported partly from scientific funds, as statutory

research and research projects

175/RMTO/RR8/2016 entitled „Porozumienie o

współpracy” concluded between Silesian

University of Technology and Opel Manufacturing

Poland.

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Received 2020-10-04

Accepted 2021-02-10

Available online 2021-02-11

Krzysztof ROCZEK M.Sc., Eng. He

received the M.Sc. degree in 2010 on

Silesian University of Technology and

now he is actual working toward his

PhD thesis. Since 2011 he has been

working as Controls Engineer at press

shop in Opel Manufacturing Poland

(previously General Motors

Manufacturing Poland). His main research interests

includes diagnostic of electrical elements and industrial

networks.

Adrian KROL M.Sc., Eng. He received the M.Sc. degree in 2015

and now he is actual working toward

his PhD thesis. He is a member of the

Institute of Fundamentals of

Machinery Design on Faculty of

Mechanical Engineering, Silesian

University of Technology. His main

research interests include diagnostic

process of large mechanical objects.

Marek FIDALI, is an associate

professor in the Institute of

Fundamentals of Machinery Design at

the Faculty of Mechanical Engineering

of the Silesian University of

Technology since 2015. He received

the Master of Science and PhD degrees

in Mechanical Engineering from

Silesian University of Technology in

1997 and 2003, respectively. His

research interests lie in technical diagnostics in the broad

sense, infrared thermography, images and signals

processing methods as well as modal analysis,

measurement systems and acoustics

Tomasz ROGALA, PhD Eng.,

Institute of Fundamentals of

Machinery Design, Silesian

University of Technology. His main

interests focused mainly on:

diagnostic knowledge modeling,

digital signal processing, application

of simulation experiments in

technical diagnostics. He has also research interest in

application of computational intelligence methods for

different engineering problems.